At least nine people were killed when severe storms led to a tornado outbreak across the United States on Wednesday, reports indicate.

According to The Weather Channel, preliminary estimates indicate that roughly 15 tornadoes swept through the nation on Wednesday.

All of the reported deaths occurred in the southeastern United States, where the damage from the storms was said to be the greatest.

Mississippi television station WREG reported that at least six people were killed in the state, including a 7-year-old boy in the town of Holly Springs. The National Weather Service said one tornado touched down south of Clarksdale and left a trail of damage that stretched some 150 miles northeast to Hardeman County, Tennessee. If the storm was continuous, the National Weather Service said it would be the longest December tornado on record in the mid-South.

The Mississippi Emergency Management Agency said tornado damage was reported in seven counties. The powerful storms injured more than 40 people statewide as they knocked down power lines, shut down multiple highways and damaged homes. The agency said there were also reports of some search-and-rescue operations.

On Thursday morning, the Mississippi governor declared a state of emergency in the affected areas.

WREG reported storms demolished an entire Clarksdale subdivision.

The Tennessee Emergency Management Agency declared a Level III State of Emergency after storms led to “isolated damage” in 11 counties. The agency said a man and a woman were killed in Perry County, one of the harder-hit areas, but had no further information. Another person died in Rhea County.

An 18-year-old woman was killed earlier Wednesday when heavy winds sent a tree crashing through a home near Atkins, Arkansas, according to the Pope County Sheriff’s Office. The death occurred in the morning, well before the tornado outbreak was at its height.

While the tornadoes and storms were most destructive in the south, there were reports of tornado damage as far north as central Indiana.

Local television station WTHR reported storms blew the roof off an animal hospital in Greenwood. No person or animal was injured.

The outbreak occurred on a day when many Americans were beginning to travel for the holidays. AAA projected a record 100.5 million Americans are expected to travel in the 12-day period that began Wednesday morning, more than 90 percent of them driving.